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6.0/4L80 Speedo Question

shooters_7

shooters_7

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For those who have already done some of these swaps for a system thats almost all computer controled. When I put a 2004 6.0/4L80 package in my 87 truck with a NP241 pass side drop, will I have an issue hooking up the mechanical speedo? Will it affect the computer at all if I run a mechanical speedo or..... I just need to know before buying parts as my truck just has the stock motor, trans and t-case in it right now. Any other issues with cruise control or other things?
 
4l80-e needs input speed and output speed to make sure stuff is working correctly.

with that there is 2 holes on case left side. these are for the sensors. now some 4x4 equiped ones will not have the back one. so you would need to fill it with a sensor to work fine. and run it as a 2x4 . as to puting a mech tcase/speedo behind it it wontt know the diffrence.

but dont quote me on this 100% this is stuff i have read and picked up along the way.
 
The transmission input & output VSS sensors should be plugged in with the engine harness. It will be telling the pcm when to shift/ lockup tc assuming your harness and computer is set up to do operate a 4l80.
your harness should also have a wire that goes to the brake switch. it is responsible for unlocking the torque converter when you step on the brakes.

not sure i understand your question.
doesn't the factory np241 have a mechanical speedo cable gear or the later years have electric speedo built into the transfer case?
So shouldn't that will work the same on your truck.\

;)
 
I thought 87 was fuel injected. That should mean that you have a VSS in the 241C like my 91 241C does. I run a 6.0L 4L80E 241C and use the factory speedo. I pulled the wire off the K5 harness for the speedo input and connected it to the VSS output on the 6.0L harness and it works fine. As far as the electronics are concerned, The VSS to the PCM is what matters. A 91 case from a Suburban is what I used (mainly for the 32 spline input for the 4L80E).
 
No, '90 was first year of VSS 241. 40 pulse output, vs. 2000PPM output of all earlier truck VSS.

I expect the 6L stuff is looking for the 40 pulse setup, but don't quote me on that. With the gear reduction in the transfercase, 4L *might* cause some problems if the transmission doesn't know it's there. (Trans will think you are going more than double your actual speed)

Just theorizing here, I've not done one of these swaps like others here have.
 
My 87 is fuel injected, but the NP241 didn't come out till 88. I believe the VSS NP241 didn't come out till 1990 like Dorian mentioned. I have the original NP208 in my truck along with the fuel injected 350. Thanks for the info as I'll hit the salvage yard up to find a 91 NP241 to use behind the 4L80. The wiring is something I've never really messed with and is what stumps me at times! Now the 91 NP241 has the attachment for the mechanical speedo correct?
 
So if you change tire sizeand or gears on an 4l80e with a 241 on a 91 that has the VSS how do you correct the speedometer?
 
'90-91 241's don't use speedometer cable. Must convert to the DRAC/electric speedo setups, or use the back half of a non-VSS 241. Personally I'd take the electric speedo route.

Tire size and gear changes are then done through the DRAC. Under the dash, near the ash tray I believe. Rectangular, thin/flat white plastic box more than likely. Plenty of posts on how to do it, essentially it's just desoldering/soldering.
 
This seems like it might be a pain in the butt! I don't know if I'll go the electronic route or not but just need to figure out the wiring. Whats the easiest way to do this and is the DRAC just an additional wiring harness I can run along with changing out the gauge cluster.
 
There are a few options for getting an output speed signal for a 4l80. None of them are that simple especially compared to a 4l60.

1: Use a 90-91 VSS transfer case. This will require an electronic speedo/speed sensor buffer as you already know. This option also requires that the low range switch be connected and wired to the PCM so it will know when low range is selected, otherwise transmission ratio codes will be stored and trans will go into limp mode.

2: Have the trans disassembled and have the tone ring installed for the output speed sensor. 4WD 4l80s built after 1996 do not have the tone ring installed nor do they have an output speed sensor installed in the case. This option while not cheap is the most direct choice.

3: Build a tone ring and modify t-case adapter to accept a speed sensor. Similar to this one for a 4l60. Click on manual hotlink for better pictures
http://advanceadapters.com/product/2404/%28P/N-716073%29-GM-VSS-Kit.html

4: Install a tone ring on rear output yoke and speed sensor on output housing like this one: http://advanceadapters.com/product/...e-VSS-Tailhousing-Kit-(1350-non-cv-yoke).html
Just like the factory VSS t-case you will have to wire the t-case low range switch to keep trans operating properly in low range.

Those are about all the options that I know of. No matter what you have to have a 40 pulse signal to make the trans work right. Any variations in the signal will cause all kinds of problems so make sure the tone ring and sensor are mounted solidly with no runout on the tone wheel and the sensor is installed with the proper air gap.
 
bigblock72 said:
There are a few options for getting an output speed signal for a 4l80. None of them are that simple especially compared to a 4l60.

1: Use a 90-91 VSS transfer case. This will require an electronic speedo/speed sensor buffer as you already know. This option also requires that the low range switch be connected and wired to the PCM so it will know when low range is selected, otherwise transmission ratio codes will be stored and trans will go into limp mode.
Click to expand...

I've been looking around for a speed buffer box for a 91 but can't find one. Of course Jet Perfomance makes one for 93s and up.
 
How about a .50 cent fix for the issue!!! I was doing searches for VSS, speed buffer box, speedometer correction.

Then I did a search for DRAC speed correction and bingo!!

http://www.tbichips.com/DRAC/

And you can order your 7 Pole DIP swith here.

http://www.allelectronics.com/make-a-store/item/DWS-7/7-POLE-DIP-SWITCH/-/1.html

You can also just buy the converted DRAC from TBICHIPS at there ebay store if you don't want to do the DIP switch upgrade yourself from here.

http://motors.shop.ebay.com/items/_W0QQ_nkwZdracQ20vssbQQ_armrsZ1QQ_fromZ

Hope it all works out for you.

edit

This place seems to list a lot of the revolutions per mile for tires.
http://www.phillipstire.com/store/cart.php?m=product_detail&p=456

/edit
 
Last edited:
You can get the DRAC out of Astro vans for probably nothing, assuming you have wrecking yards close by. Astro's have them up near the center air condition vent at the top of the dash.

If the dash pad is out, it takes about two minutes to pull them.

Gotta do some work, but even buying the DRAC from someone you still need the connectors on the DRAC and the transfercase, and the wiring to the DRAC from the VSS is a "twisted pair".
 
So just using the speed sensors on the side of the 4L80 like sweetK30 said and going with a non-VSS t-case is the easier way? I'm not up for all the extra wiring. I just want to keep it as simple as possible and if the 4L80 is 96 and up then doing bigblock72 second option is the better way to go in order to skip all the additional wiring.

2: Have the trans disassembled and have the tone ring installed for the output speed sensor. 4WD 4l80s built after 1996 do not have the tone ring installed nor do they have an output speed sensor installed in the case. This option while not cheap is the most direct choice.
 
dyeager535 said:
You can get the DRAC out of Astro vans for probably nothing, assuming you have wrecking yards close by. Astro's have them up near the center air condition vent at the top of the dash.

If the dash pad is out, it takes about two minutes to pull them.

Gotta do some work, but even buying the DRAC from someone you still need the connectors on the DRAC and the transfercase, and the wiring to the DRAC from the VSS is a "twisted pair".
Click to expand...

I assume you are talk to the OP as I have a DRAC in my suburban. I just need to be upgraded to the DIP switch so I can input the correct 7 digit binar code that corrects the speedometer for my tires and gear set.

What year Astro van will work??
 
Actually I wasn't, you are talking about looking for a speed buffer box, if it's unclear, the DRAC *is* the buffer on a stock GM truck setup. Cars and maybe later trucks did use a "buffer" in some cases.
 
dyeager535 said:
Actually I wasn't, you are talking about looking for a speed buffer box, if it's unclear, the DRAC *is* the buffer on a stock GM truck setup. Cars and maybe later trucks did use a "buffer" in some cases.
Click to expand...

Yup, I had read about a speed buffer box which I think people were refering to a the VSS Buffer in the 92 and up. Jet performance sells a box that you can connect to that to adjust the speedometer.

The more I read, the more I learned. What I learned was my 91 has a DRAC that has 7 pin slots. You can either change the pins on them or sodler in a DIP switch.

All I needed to find out was how to correct a 91s speedometer. Once I learned how easy that part was I want to share it.
 
Gotcha...it is very easy indeed.

My opinion is that if you are just going to throw a new tire on there that is a different size and leave it alone from there out, soldering is "good enough". If you expect to make a lot of changes with gearing and tires, it's going to be easier in the long run to solder in the DIP switch.
 
dyeager535 said:
Gotcha...it is very easy indeed.

My opinion is that if you are just going to throw a new tire on there that is a different size and leave it alone from there out, soldering is "good enough". If you expect to make a lot of changes with gearing and tires, it's going to be easier in the long run to solder in the DIP switch.
Click to expand...

Yeah, I'm kind of rethinking the DIP switch and was even thinking about picking up a second DRAC to sodler on. That way if I screw it up I still have the stock one.
 
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